Pepsinogen (inactive form) is converted into the active form of the enzyme pepsin with the help of which of the following compounds?

In human beings,which of the following parts of the alimentary canal act as the site of initiation of digestion of proteins,fats and carbohydrates,respectively?

Where does protein digestion primarily occur?

Identify the enzymes at $A$ and $B$ which hydrolyze the substrates.
Proteins $\xrightarrow{ A }$ $\begin{array}{c}\text{peptones} \\ + \\ \text{proteoses}\end{array}$ $\xrightarrow{ B }$ polypeptides

Which of the following guards the opening of the hepatopancreatic duct into the duodenum?

Digestion of starch starts from the mouth, whereas $A$ is the site of digestion mainly for $B$. Choose the correct combination of options to complete the given statement.